The present invention relates to a new and improved pneumatic vehicle tire.
The present invention relates more specifically to a new and improved pneumatic vehicle tire comprising a radial ply carcass, two side walls each lining or covering a respective lateral region of the carcass, a tread member covering an apex or crown region of the carcass, and a belt comprising at least one rubberized cord ply embedded between the tread member and the apex or crown region of the carcass. The tread member comprises a base layer positioned closer to the tire axis i.e. the axis of rotation of the tire and a cap layer arranged on top thereof.
Such structure substantially corresponds to a conventional tire having a tread member which is "doubled", i.e. composed of two layers. A number of different patents have been published with respect to such type tread members.
A tire as known, for example, from U.S. Pat. No. 3,157,218, granted Nov. 17, 1964, comprises a tread member having a base layer which prevents, due to its chemical-physical properties, too great heat build-up caused by the expanding and compressing or so-to-speak pumping movement of the tire during use. Such construction is known in a somewhat modified form in diagonal ply tires, however, is selected there for reasons of the technological process. In the one-step construction of diagonal ply tires, the side walls comprising a single semi-finished material can be applied to the non-crowned carcass and only thereupon is there prepared the actual tread surface. Thus, the portion of the semi-finished material forming the side walls is positioned below the actual tread surface, and thus, is located in the position of a base layer.
A pneumatic tire as described, for example, in U.S. Pat. No. 3,931,844, granted Jan. 13, 1976, comprises a cushion-like support under the tread member. This support is more supple or softer than the rubber mixture of the actual tread member and which extends over the tire width. In the region of the equatorial plane of the tire the support has its greatest thickness and has, however, only a very small thickness in the region of the tire shoulders. By virtue of such a structure a uniform tire wear and an improved traction are intended to be achieved.
In another tire construction as described, for example, in German Pat. Publication No. 3,008,713, published Sept. 24, 1981, a plate is arranged between the belt and the actual tread member. The plate has a Shore hardness in the range of about 40 to 50 and a resilience or rebound elasticity in the range of about 60 to 70 and it possesses a width which corresponds to about 60 to 70 percent of the width of the belt. It is the object of this tire structure to reduce the rolling resistance and the heat build-up.
A tire as described, for example, in German Patent Publication No. 3,046,716, published Sept. 17, 1981, comprises a tread member composed of an inner and outer ply which have different hysteresis loss indices. Also in this case the object is to reduce the rolling resistance of the tire and thereby the energy loss. At the same time a distinct geometrical configuration is described in this publication.
A tread member subdivided in the same way and as described, for example, in German Pat. Publication No. 3,045,765, published June 11, 1981, has a base layer which is designated as a dampening caoutchouc layer. This layer has an elasticity loss modulus in the range of 2 to 12 kg/cm.sup.2 and a resilience or rebound elasticity in the range of 60 to 85 percent. Also this construction is concerned with the improvement of the rolling properties just as in German Pat. Publication No. 3,002,360.
In the tire as known, for example, in such German Pat. Publication No. 3,002,360 a base layer and a cap layer are described which have different values of the resilience or rebound elasticity for improving the rolling properties of the tire.
It is furthermore known in radial ply tires for trucks to arrange a covering layer of highly dampening rubber, which covering layer is termed "tire buffer". Frequently, this tire buffer comprises only two bands or strips which are arranged to extend over the belt edges, and thus, have a belt edge protecting function. Rubber mixtures suited therefor have a very small hardness like, for example, a Shore A hardness of 50 and also have a very small stress value like, for example, .sigma. 150=1 MPa. Such "poor" properties are required for the function as a tire buffer and do not negatively affect the properties of the tread member due to the small thickness thereof which is, for example, in the range of 2 to 4 millimeters. Such rubber mixtures or formulations for tire buffers would be unsuited for base layers.
It is substantially the object of the known tire constructions to maintain the rolling resistance, and thus, the energy loss at the smallest possible value and to also prevent excessive heat generation during use. This object is partially satisfied by the tire constructions as mentioned hereinbefore. However, it has been found that the intended reduction in the rolling resistance is not satisfactorily obtained with the known constructions when the tire is driven through curves. The effect is particularly negative also for the reason that radial ply tires have their highest bearing pressure in the region of the shoulders and that the highest contributions to the reduction in the rolling resistance can be achieved in these very locations.